Soluble Interleukin-15 Receptor α (IL-15Rα)-sushi as a Selective and Potent Agonist of IL-15 Action through IL-15Rβ/γ

Abstract

Interleukin-15 (IL-15) is crucial for the generation of multiple lymphocyte subsets (natural killer (NK), NK-T cells, and memory CD8 T cells), and transpresentation of IL-15 by monocytes and dendritic cells has been IL-153 is a cytokine that was originally described, like IL-2, as a T cell growth factor (1). Both cytokines belong to the four ␣-helix bundle family, and their membrane receptors share two subunits (the IL-2R/ IL-15R ␤ and ␥ chains) responsible for signal transduction (2). The IL-2R␤/␥ complex is an intermediate affinity receptor for both cytokines that is expressed by most NK cells and can be activated in vitro by nanomolar concentrations of IL-2 or IL-15. The high affinity IL-2 and IL-15 receptors, such as those expressed on activated T cells, can be activated with picomolar concentrations of either cytokine, and additionally contain their own private ␣ chain (IL-2R␣ and IL-15R␣) that confers cytokine specificity and enhances the affinity of cytokine binding (3).Both cytokines play pivotal roles in innate and adaptative immunity. Whereas initial in vitro experiments have shown a large functional overlap in the effects of the two cytokines (induction of the proliferation and cytotoxicity of activated lymphocytes and NK cells, co-stimulation of B cell proliferation and immunoglobulin synthesis, and chemoattraction of T cells) (1, 4 -6), more recent experiments have indicated that they can exert complementary or even contrasting actions in vivo. Whereas IL-2 or IL-2R␣ knock-out in mice was associated with autoimmune phenotypes with increased populations of activated T and B cells, IL-15 and IL-15R␣ knock-out resulted in specific defects in NK, NK-T, intraepithelial lymphocytes, and memory CD8 T cells (7,8). Furthermore, IL-2 promotes peripheral tolerance by inducing activation-induced cell death, whereas IL-15 inhibits IL-2-mediated activation-induced cell death (9), and, unlike IL-2, IL-15 is a survival factor for CD8 memory T cells (10). In line with these observations, it has been suggested that the major role of IL-2 is to limit continuous expansion of activated T cells, whereas IL-15 is critical for initiation of T cell division and survival of memory T cells (11). A novel mechanism of IL-15 action described recently is that of transpresentation in which IL-15 and IL-15R␣ are coordinately expressed by antigen-presenting cells (monocytes and dendritic cells), and IL-15 bound to IL-15R␣ is presented in trans to neighboring NK or CD8 T cells expressing only the IL-15R␤/␥ receptor (12). As a co-stimulatory event occurring at the immunological synapse, IL-15 transpresentation now appears to be a dominant mechanism for IL-15 action in vivo (13, 14) and appears to play a major role in tumor immunosurveillance (15).The IL-15R␣ and IL-2R␣ subunits form a sub-family of cytokine receptors in that they comprise extracellular parts, so called "sushi" structural domains (one in IL-15R␣ and two in IL-2R␣), at their N terminus, which are also found in complement or adhesion molecules (16). In both cases, these ...

An Antibody Fusion Protein for Cancer Immunotherapy Mimicking IL-15 trans-Presentation at the Tumor Site

“…In solution, constructs presenting IL-15 in combination with the IL-15Ra domain (RD) stimulated more efficiently the proliferation of IL15Rbg-expressing Mo7e cells. This observation was in accordance with the data reported for the (RLI) fusion protein and the IL-15/IL-15Rasushiþ complex, showing enhanced cytokine effect on Mo7e cells in comparison with IL-15 alone (32,33). In regard to the stimulation of the high-affinity receptor IL-15Rabg, the presence of the RD fragment in the fusion proteins decreased the cytokine activity of the constructs in solution, independently of the presence of the scFv.…”

“…Structural studies identified the "sushi" region in the IL-15Ra as the main responsible element for IL-15 binding (31). In vitro, soluble complexes of recombinant IL-15 and the IL-15Ra sushi domain were described to induce agonistic effects on the intermediate affinity receptor (IL-15Rbg), inducing stronger proliferation than IL-15 alone (32). This effect could be even enhanced when the sushi domain of IL-15Ra was extended by 13 amino acids of the exon 3 (IL-15Rasushiþ), thereby increasing the binding affinity for IL-15 (33).…”

“…This effect could be even enhanced when the sushi domain of IL-15Ra was extended by 13 amino acids of the exon 3 (IL-15Rasushiþ), thereby increasing the binding affinity for IL-15 (33). Although this complex showed reduced bioactivity on high-affinity receptor IL-15Rabg-expressing cell lines, the combination of IL-15 and IL-15Rasushiþ into a fusion protein (RLI) retrieved a molecule that presented maximal enhancement of IL-15Rbg stimulation without losing stimulatory capacity for IL-15Rabg (32,33). Furthermore, the fusion protein (RLI) showed efficiency in vivo by inducing antitumor effects in diverse mouse models (26).…”

Le renouveau de l’interleukine 2

“…Son intérêt, comme molécule antitumorale, a été validé dans de nombreux modèles expérimentaux, et plusieurs essais cliniques ont été initiés chez l'homme dans différents contextes tumoraux [37]. Plusieurs stratégies sont à l'étude pour renforcer son action sur l'hétérodimère IL-2Rβ/γ, incluant l'utilisation de complexes IL-15/ IL-15Rα solubles ou la molécule RLI (IL-15-IL-15 receptor fusion protein) [38]. Dans la perspective de l'induction de tolérance aux greffons et de traitement des maladies auto-immunes et inflammatoires, des stratégies sont entreprises afin de renforcer la spécificité d'action de l'IL-2 pour les cellules Treg qui présentent de manière constitutive le récepteur trimérique IL-2Rα/β/γ, par rapport aux lymphocytes NK et les T CD8 mémoires qui sont eux porteurs de l'hétérodimère IL-2Rβ/γ (Figure 3B).…”

The tumor immunosuppressive microenvironment impairs the therapy of anti-HER2/neu antibody

“…It is reported that the complex of IL-15Rα and IL-15 is a strong stimulator for the responses of NK cells and CD8 + T cells (Dubois et al, 2008;Epardaud et al, 2008;Han et al, 2011). We prepared IL-15R/IL-15 fusion protein by fusing IL-15 receptor α sushi domain with IL-15 (Mortier et al, 2006). To measure the activity of IL-15R/IL-15 fusion protein in vivo, mice were hydrodynamically injected with IL-15R/IL-15 plasmid or control plasmid.…”